Vehicle automatic transmissions include one or more gear sets, consisting of an inner sun gear, intermediate planet gears and their carrier, and outer ring gear. Various components of the gear set are held or powered to change the gear ratio. Reverse gear is provided by holding the planet carrier stationary relative to the transmission housing. When the sun gear is powered, the planet gears act as idlers, spinning around their own axes, but not traveling. Consequently, the ring gear turns in reverse. Another consequence of grounding the planet carrier is the familiar "lug down" feeling experienced in reverse when the driver lets up on the accelerator.
The most common commercially applied holding mechanism is the disk pack clutch. An interleaved set of plates and friction disks normally turn past one another without contact, bathed in a continual flow of lubricant. Upon a signal for gear change, a piston pushes the plates and friction disks together. While they work well and reliably, typical disk pack clutches occupy a good deal of axial room, and are heavy, with a large number of components.
Another known holding mechanism is a shiftable one way roller clutch, which can be used in place of the typical disk pack clutch. By shiftable, it is meant that the roller clutch can be selectively disabled, preventing it from locking up in either direction. When activated, it can prevent the planet carrier from turning relatively to the transmission housing in the one relative direction that the sun gear could otherwise cause it to rotate. This has the same net effect as the disk pack clutch, as far as creating reverse gear. However, unlike the disk pack clutch, when the accelerator is eased, the planet carrier can effectively overrun the transmission housing in the other direction, preventing lug down.
An example of a roller clutch designed for such an application may be found in U.S. Pat. No. 3,054,488 to General et al. The overrunning clutch disclosed there is a leg type roller clutch, with an outer cam race that pilots on an inner pathway. The mechanism that shifts the rollers is a phasing ring that carries a series of so called pawls, one for each roller, which extend axially in between the races. When the phasing ring is twisted back and forth, the pawls push the rollers back and forth, in or out of the cam wedges, enabling and disenabling the clutch. The phasing ring is described as being shifted by pressurized fluid that is pumped through passages drilled through the outer race and into the space between the races. No means for actually pumping in and withdrawing the fluid pressure is disclosed, however. So, while the general concept of a shiftable one way clutch to replace a disk pack in an automatic transmission is disclosed per se, a practical means of in fact incorporating it into the transmission and positively shifting it is not disclosed. The system apparently never achieved actual, commercial application.